A few weeks back I did some work on an Alpine MRV-1000.It had some blown output transistors(2SA1265N),4 blown power supply fets(irfz44n), and a bad zener diode.After replacing the parts mentioned above it worked great for about three weeks until yesterday when it had another blow out.I had just turned on my car and went to turn up the volume and was welcomed by weak output.The output then became solid for about two seconds before it stopped playing all together.Upon quick inspection I found that one of the same 2SA1265Ns that I had replaced previously had bit the dust once again.The newly replaced power supply fets survived this time.Now I have enough parts to make this repair again but I'm wondering if there is possibly something that I missed last time.On the last repair I only replaced the 2SA1265Ns in that channel but left the original complimentary 2SC3182Ns.Could this have caused the problem potentially?Or is it maybe just bad luck?I'd love to get this thing playing again for good so if anyone has any ideas as to what I might have missed I'd like to hear them.

If either, one of the base resistors, or one of the emitter resistors is out of tolerance, it could cause one transistor to pass more current than the one in parallel with it.

Are you sure the mating surface was flat and clean. A tiny piece of debris can prevent proper mating of the transistor/insulator/heatsink.

If you have a scope, drive the amp into a speaker load (try several different speakers) and look for noise/oscillation on the output. If there is any sign of oscillation, that can cause the outputs to heat up and fail.

I know this post is forever old but I just recently got time to work on this amp again.Given your experience Perry what are some things I could look for that could have potentially caused this last failure?Is it worth it to just replace all the outputs in that channel and cross my fingers?Or do you think there may potentially be a bigger issue?

It's always best to replace all of the outputs in a channel when any others in that channel have failed.

As for suggestions, see my previous post in this thread. Check the emitter resistors very carefully.

Make sure that there is sufficient clearance between the leads of the transistors and the heatsink (or other conductive components).

Are you sure it's not failing due to a wiring fault (possibly intermittent) in the vehicle? If you're not sure and cannot find a fault in the vehicle, you may want to insert 3A fuses in the speaker leads (on the wires used for bridging).

I haven't checked the wiring in the car but I have had several different amps in there(even a few other repairs) without any problems.Will I have to remove those resistors from the board to get a true reading or can I get a good reading by placing my meter leads in parallel with the resistor mounted in the board? Are the emitter resistors the large white ones near the output transistors? Also I was wondering about the small transistors directly to the left and right of the outputs. Should these all be replaced along with the larger output transistors?

You can check the resistors in the circuit (after you've removed the shorted transistors). Sometimes there are other components in parallel with the resistors which can cause erroneous readings. For definitive readings, you should pull one end of the resistor. In this case, there is nothing connected to one end of the base resistor when the transistor is out of the circuit so there is no reason to pull one end.

The emitter resistors can be checked in the circuit. The emitter resistors (white ceramic components) are 0.1 ohms per resistor (2 resistors per housing). Check them from the middle leg to the outer legs. They should be the same. You will have to hold your meter on them for a few seconds to allow it to stabilize.

The smaller transistors on the outside of the outputs are the driver transistors. You should check them. If you have to order new outputs, order new drivers and replace them. It's unlikely that the drivers caused the outputs to fail but you've found no other reason for them to have failed the second time.

The small transistor between the outputs is the biasing transistor. If there are bad connections on the biasing transistor, that could cause the outputs to overheat and fail.